Aerosols are useful in a wide variety of applications. For example, aerosols have been used to treat respiratory ailments, or to deliver medicaments, by providing sprays of finely divided particles of liquids and/or solids, such as powders, liquid medicaments, and the like, which are inhaled by patients. Aerosols are also useful, for example, for delivering desired scents to rooms, applying scents to the skin, and delivering paints and lubricants.
There are various known techniques for generating aerosols. For example, U.S. Pat. Nos. 4,811,731 and 4,627,432 disclose devices for administrating medicaments to patients that include a capsule, which is pierced to release medicament in powder form. The user inhales the released medicament through an opening in the device. Medicaments in liquid form have been delivered by generating aerosols with a manually operated pump. The pump draws liquid from a reservoir and forces it through a small opening to form a fine spray.
Alternatively, medicaments have been delivered by generating an aerosol including liquid or powder particles using a compressed propellant, which entrains the medicament. Such inhalers are usually operated by depressing an actuator to release a charge of the compressed propellant, which contains the medicament, through a spray nozzle, allowing the propellant encapsulated medicament to be inhaled by the user. However, it is difficult to properly synchronize the inhalation of the medicament with depression of the actuator. Further, desired quantities of medicament or other materials are not suitably delivered by this method.
Many aerosol generating devices also are unable to generate aerosols having an average mass median aerosol diameter (MMAD) less than 2 to 4 microns, and to deliver high aerosol mass flow rates, such as above 1 milligram per second, with particles in the size range of 0.2 to 2.0 microns. A high aerosol mass flow rate and small particle size are particularly desirable for enhanced penetration into the lungs during medicament administration, such as for asthma treatment.
Larger particles generated by inhalers may be deposited in the mouth and pharynx of the patient, rather than inhaled into the lungs. In addition, larger inhaled particles may not penetrate into the lungs as deeply as desired for certain applications.
Therefore, there is a need for an aerosol generating device that can provide different aerosol size distributions of aerosols, such that the device can be adapted to the different needs of a patient. Moreover, there is a need for an aerosol generating device that provides controlled adjustability of the aerosol size distribution of aerosols that it produces.